Automotive vehicles have, associated with their windshield and often their rear window, glass wipers including two blades connected to a drive mechanism for alternate turning motion.
The wiping or squeegee portion includes a flexible wiping blade usually of rubber having an edge encased in a flexible metal strip and a support assembly for the blade connected to the drive mechanism for alternately turning the wiper.
The support assembly usually comprises a principle or main yoke having means for attaching to a wiper arm by means of which the wiper can be driven, and yokes pivotally connected directly or indirectly to the main yoke.
Usually, the main yoke pivotally supports an intermediate yoke at an end of each of its branches, and each intermediate yoke pivotally supports a secondary yoke at the end of each of its branches.
In this case the flexible blade or wiper strip is attached to the ends of the secondary yokes.
The main yoke is a carrier yoke which transmits the force that presses the wiper against the glass. The intermediate yokes are at the same time, support yokes and carrier yokes on which the secondary yokes are mounted.
In the case of automotive vehicle windows such a windshields or rear windows which are very curved, it is necessary to use a wiper blade of great suppleness capable of assuming the contour of the glass whatever may be the position of the wiper blade relative to the curved surface, under the effect of the pressure force transmitted by the wiper arm.
The use of a blade wiper of great suppleness and the pivotal mounting of the supporting yokes on the carrier yokes usually permits avoiding the separation of the supple wiper relative to the glass which occurs with a defective wiper.
However, in the case of very curved windows, a portion of the outer extremity of the wiping blade can be found to be raised relative to the surface of the glass in certain positions of the blade during use.
In addition, the wiping devices for windows of automotive vehicles can be equipped with a stop positioning system called stop-parking which allows the protection of the wiper blades and prohibits removal when the blades are in a rest position, particularly when the vehicle is standing. The principle of operation of stop-parking is the following: by increasing the angle of sweep of the blades, the system for stop-parking positioning of the wiper blades permits the blades to be placed under the hood of the motor. This displacement in the stop-park position can be accompanied by a relaxing of the pressure force of the blades on the window, due to ramps or abutments assuring a predetermined lifting of the blades or a relaxing of the pressure force exerted by the wiper arms.
The outer end of the blade is then found to be lifted with respect to the surface of the glass such that on return of the blade to the active position, contact of the end of the blade with the glass is not very certain.